The entire propulsive capacity of solid propellant rocket motors is usually spent during the combustion process of one mass of solid propellant. This is for the reason that, once a solid propellant is ignited, it is very difficult to stop the combustion process until the entire mass of ignited propellant has been consumed.
It is known to provide a solid propellant rocket motor with the ability to fire more than once. Such a rocket motor with a “start-stop-restart” capability is commonly called a “pulsed” rocket motor. It includes, within the same case, two or more solid propellant units, such as a boost grain and a sustain grain, separated by a membrane seal structure that enables the ignition of the propellant units to be independent of each other. In this manner, discreet impulses are available upon command. Quite often, the solid propellant units are positioned in tandem with each other; that is, with one solid propellant unit, or grain, forward of the other. Normally, the aft unit will burn to completion before the forward unit is ignited. However, neither the prior art nor this invention is limited to only two stages, but may include any number of tandem stages sequentially ignited.
This invention relates primarily to relatively small solid propellant powered missiles that are fired from a “bus” such as a larger missile or an airplane. For example, a large missile carrying up to 50 or more decoys (simulating reentry vehicles for example) may be surface-launched. Each decoy may be a solid propellant powered rocket that will be launched from the bus toward a specific target. In this manner, all of the decoys when launched will simulate an attack on a plurality of targets. It then becomes difficult for an enemy to distinguish between decoys and actual warheads. In order to simulate actual warheads, it is necessary to be able to control: (a) bus release time; (b) the angle of attack; (c) the velocity changes of the missile as it enters the Earth's atmosphere; and (d) other factors such as radar image. It is often desirable to control the signature profile of the plume, as well as the thrust profile. The term “mass discharge profile,” as used herein, includes both.
A bus may launch these smaller missiles over a lengthy portion of its flight path. These flight path portions may have widely varying velocities, directions of movement, locations, and elevations. Furthermore, the actual flight path of the bus may vary somewhat from the planned flight path. All of these factors must be taken into account to achieve the desired trajectory and velocity for each of the decoy missiles. Furthermore, the desired trajectory and velocity may differ for each decoy.
As previously explained, rocket motors powered by solid propellant grains have an important limitation. This is that, once ignited, each grain burns to completion. In the prior art, missiles with multiple-stage motors are known, but the stages are either ignited simultaneously or each stage is ignited after prior stage combustion is completed (so-called “pulse” motors).
It is, therefore, an object of the present invention to provide a multiple-stage solid propellant rocket motor wherein preselected thrust, velocity, and trajectory are achievable with a given mass of propellant.
Another object is to provide such a motor wherein the variable factors may be preset prior to launch of the missile from the bus.
Another object is to provide such a motor wherein the variable factors may be preset prior to launch of the bus vehicle.
Other objects, features, and advantages will become apparent from the following description and appended claims.